Lignite Properties and Boiler Performancemicrobeam.com/wp-content/uploads/2015/02/Benson-EGC-2015... · 2015. 2. 3. · Lignite Properties – Managing to improve performance Lignite

Lignite Properties and Boiler Performance

Energy Generation Conference:Reducing CO2 Intensity in Power Plants

Steve BensonPresented at the Energy Generation Conference

Bismarck, ND January 28, 2015

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Contact InformationMicrobeam Technologies, Inc.

Email: [email protected]

North Dakota Office:4200 James Ray Drive, Ste. 193

Grand Forks, ND 58201Tel.: (701) 777-6530Fax: (701) 777-6532

Minnesota Office:14451 Hwy 7, Ste. 202

Minnetonka, MN Tel.: (701) 738-2447Fax: (763) 273-1347

Steve’s Cell: (701) 213-70702

Background of Microbeam Technologies, Inc. Mission: To provide advanced analysis and interpretations of the

impacts of fuel properties on plant fireside performance. Founded: 1991 and began performing analysis of samples using

advanced electron microscopy methods in 1992 Growth: Expanded laboratory in 2004 to include high-temperature

small scale test equipment – slag/ash behavior in combustion/gasification systems; New office in Minneapolis in 2014

Clients: Equipment developers, gasification (syngas, methane, fertilizers), electric utilities, state and federal government, coal companies, consultants, universities, law firms, research organizations, and others

Work: Conducted >1450 projects worldwide, >7000 samples analyzed

Staff: – experience with fossil/renewable fuels conversion and environmental control systems – research/development –commercialization – education – problem solving focus

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Overview Lignite Properties – Managing to improve performance Lignite Preparation Energy Conversion – Combustion/Boilers Fate of Lignite Impurities

Ash formation Slag Ash deposits – wall slagging and convective pass fouling Fine particulate

Boiler Design for Lignitic Coals Predictive Tools – use to improve performance and reduce

CO2 intensity Summary

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Lignite Properties High Moisture High oxygen content – organically

associated impurities Form and abundance of impurities – ash-

forming materials, sulfur High reactivity Non-caking

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Coal Impurities No ash in coal! – ash-forming components or

impurities Particles – minerals and other materials – Electron

microscopy – size, composition, abundance (3000 particles)

Inorganic elements associated with coal matrix –elements (alkali and alkaline earth elements) –Chemical fractionation – abundance of organically associated elements

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Sources of Impurities in Lignite During Formation From original plant material Influx of sand clays by wind and water Ground water flow Mineralization

During Mining Overburden, partings, underclay

incorporated into lignite

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Association of Impurities in Lignite

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Lignite Preparation

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Crushers and Pulverizers Cyclone Fired Boilers -3/8 in

Fluidized bed -1/4 in

Pulverized Coal 80% -200 mesh (74 µm)

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Impurities in Coal Higher mineral content Quartz and clays Ca organically

associated Clay mainly included

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Figure Point/Area Description Na Mg Al Si S K Ca Ti Fe Zr O 5 1 Excluded mineral 0.0 0.1 0.8 59.0 0.4 0.3 0.2 0.1 0.1 0.7 38.5

2 Included mineral 0.0 0.2 27.9 38.3 1.1 0.7 0.9 0.1 0.6 1.3 28.93 Included mineral 0.0 0.2 24.4 30.6 0.6 0.4 0.3 0.2 0.2 0.9 42.24 Excluded mineral 0.0 0.1 1.0 53.6 0.3 0.2 0.1 0.1 0.1 0.5 44.15 Excluded mineral 0.1 0.2 0.8 49.6 0.3 0.2 0.2 0.1 0.1 0.6 47.96 Included mineral 0.0 0.0 0.4 62.3 0.1 0.2 0.1 0.1 0.2 0.2 36.57 Included mineral 0.3 0.3 1.0 46.6 0.4 0.1 0.1 0.0 0.1 0.6 50.48 Coal matrix 0.0 0.0 2.7 4.9 18.7 1.4 42.1 1.9 4.9 3.4 20.19 Included mineral 0.0 0.0 0.5 23.8 0.2 0.1 0.2 0.1 0.2 55.2 19.9

6 1 Included mineral 0.0 0.1 26.6 31.8 0.3 0.2 0.2 0.1 0.3 0.6 39.92 Included mineral 0.0 0.0 9.2 49.2 0.4 5.8 1.3 2.6 3.1 0.2 28.33 Included mineral 0.0 0.1 18.1 41.4 2.6 10.3 4.5 2.5 2.4 2.2 15.94 Included mineral 1.1 1.2 2.6 40.6 1.2 0.5 1.1 0.1 0.2 1.5 50.05 Excluded mineral 0.1 0.0 0.7 88.4 0.0 0.4 0.4 0.3 0.4 0.1 9.36 Excluded mineral 0.0 0.0 0.7 60.0 0.2 0.2 0.1 0.1 0.2 0.5 38.07 Included mineral 0.0 0.0 0.7 57.6 0.0 0.2 0.3 0.3 0.4 0.1 40.38 Included mineral 0.1 0.4 22.2 36.2 2.4 1.3 1.8 0.2 0.5 2.3 32.69 Excluded mineral 3.2 1.0 22.2 29.1 0.8 3.0 0.8 0.7 0.8 0.9 37.6

Excluded Average 0.6 0.2 4.4 56.6 0.3 0.7 0.3 0.2 0.3 0.5 35.9Included Average 0.1 0.2 13.3 43.5 0.9 2.0 1.0 0.6 0.8 1.0 36.5

Mineral Types in Coal

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Conventional Analyses on CoalsOxides Antelope Rawhide Caballo ND Lignite

SiO2 25.6 28.3 26.7 21.2Al2O3 13.3 14.1 16.6 8.5Fe2O3 10.2 5.3 5.1 7.7TiO2 1.3 1.0 1.1 0.6P2O5 0.6 1.2 1.7 1.1CaO 24.8 27.3 25.1 19.6MgO 6.4 9.3 8.0 8.2Na2O 1.3 1.1 1.0 8.7K2O 0.1 0.3 0.3 0.4SO3 16.2 12.3 14.4 23.9

Moisture 23.5 30.7 29.7 36.8Vol. Matter 36.6 31.4 32.3 30.4Fixed Carbon 36.2 33.6 33.6 27.5Ash 3.8 4.4 4.5 5.4

Hydrogen 6.3 6.4 6.4 7.1Carbon 52.0 47.9 48.9 41.4Nitrogen 0.8 0.6 0.7 0.5Sulfur 0.3 0.3 0.3 0.6Oxygen 36.9 40.4 39.2 45.0Ash 3.8 4.4 4.5 5.3

Btu 8350 8262 8508 7252

Ash Composition,Wt % Equivalent Oxide

Proximate,Wt %

Ultimate,Wt %

Heating Value,BTU/lb

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Advanced Versus Conventional ASTM Analysis

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Energy Conversion Systems –Combustion - Boilers

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Overall Ash Formation and Deposition Processes

Benson, S.A., Jones, M.L. and Harb, J.N. Ash Formation and Deposition--Chapter 4. In: Fundamentals of Coal Combustion for Clean and Efficient Use, edited by Smoot, L.D. Amsterdam, London, New York, Tokyo: Elsevier, 1993, p. 299-373.

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Rocket Science?

Combustion – Pulverized Coal Flame – Test Burner

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Pulverized Coal Combustion Systems

Wall-fired (B, C) Tangential-fired (A)

Primary Air and Coal

Secondary Air

Primary Air and Coal

Secondary Air

Primary Air and Coal

Secondary Air

(A) (B) (C)

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Cyclone-Fired Coal Combustion Systems

Secondarysuperheater

Reheat superheater

Primary superheater

Economizer

Platers(suspended

surface)

Centrifugal Action

Secondary Air

Slag

Slag tap

CoalAir

Air

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Fate of Lignite Impurities

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Ash Formation in a Coal Flame

Molten Ash Droplets

Solid Particles

Na, K, SO2NOx, Hg etc.

Vapors

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Pulverized Coal Fired –Ash Formation Processes

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Transformations of Impurities in Boiler

• Size of ash particles• Composition of ash particles• Physical properties of ash particles• Deposits formation and collection of

ash particles

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Ash Formation – Partitioning

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Ash Particle Size and Composition Distribution

Na and Ca rich

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How do deposits form in boilers? Transport of particles and vapor phase

material to the surface Sticking to the surface – sticky material

formation

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Ash Transport to Heat Transfer Surfaces The transport of intermediate ash species

(inorganic vapors, liquids, and solids) is function of: State and size of the ash species System design – burner type, heat transfer

surface configuration System conditions, such as gas flow

patterns, gas velocity, and temperature

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Ash Transport Mechanisms

eddy

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Sticking and Bonding Phases

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Silicate Viscosity: Slag Flow, Particle Sticking, Deposit Strength

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Burners

Slagging

Convective pass fouling

High temperature

Low temperature

Wall Slagging (high-temperature bonding phases) Indicates propensity of

deposits to accumulate on the radiant walls of a boiler

Temperatures from 2000 to 3000°F (1093 to 1649°C).

Wall Slagging

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Deposit Thickness T-fired boiler

Ma, Inman, Lu, Sears, Kong, Rokanuzzaman, McCollor, Benson, Fuel Processing Technology 88 (2007) 1035–1043. 33

Burners

Slagging

Convective pass fouling

High temperature

Low temperature

Silicate (high temperature) Occurs in high-temperature

convective pass Temperatures between 1600 and

2400°F Silicate-based deposits

Sulfate (low temperature) Low-temperature convective pass Temperatures between 1000 and

1700°F Sulfate-based deposits

Convective Pass Fouling

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Deposit thickness (mm) on super heater division panel

Ma, Inman, Lu, Sears, Kong, Rokanuzzaman, McCollor, Benson, Fuel Processing Technology 88 (2007) 1035–1043.

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Convective pass deposits

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Deposit Sampling and Analysis

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Boiler Design for Lignite

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Effects of Rank and Coal Type on Boiler Sizing

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Important Design Criteria for the Furnace Net heat input per furnace plan area (Btu/hr-ft2) Vertical distance from top fuel nozzle to furnace arch

Distance is function of furnace width and depth Furnace dimensions must provide residence time to:

Properly burn fuel Cool the combustion products

Function of body of the boiler (radiative heat transfer)

Important Factors in Convective Pass Fouling Erosion can be diminished by minimizing gas velocities. Fouling can be reduced by:

Sootblowing- Air for low-fouling situations- Steam for high-fouling situations- Pulsed detonation - Acoustic horns

Lower heat release rates (large furnace volume) Greater number of wall blowers to minimize wall slagging Higher excess air levels Greater number of retractable sootblowers in the convective pass Increased tube spacing Additives

Convective Pass Design

Design Evolution for Boilers Firing North Dakota Lignite Coals

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Predictive Tools

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Ash Behavior IndicesExample

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Example: Predicted High-Temperature Fouling for Lignite Blends at four temperatures

Day 2 Lignite blendfired under 4 conditions

Day 3 Lignite blend fired under5 conditions

Day 4 Lignite blend fired Under 4 conditions

Day 1 BaselineLignite Blend

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Comparison of observed with predicted fouling behavior

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Summary - Lignite Property Impacts Moisture – lowers heating value, increases volume of gas in

combustor, changes where heat is absorbed Volatile matter – lower volatile matter decreases ability to stage

and reduce NOx Ash – increase lowers heating value

Higher basic ash (Na, Mg, Ca, K, Fe) (low ash contents) – fine particle formation, reflective ash in boiler, higher furnace exit gas temperatures, increased convective pass fouling, higher opacity

Higher acidic ash (Si, Al, Ti) (higher ash contents) – larger ash particle formation, wall slagging, high-temperature convective-pass fouling, lower low-temperature convective-pass fouling, lower opacity

Blending – significant opportunity to improve the efficiency/reliability and decrease CO2 intensity

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Contact InformationMicrobeam Technologies, Inc.

Email: [email protected]

North Dakota Office:4200 James Ray Drive, Ste. 193

Grand Forks, ND 58201Tel.: (701) 777-6530Fax: (701) 777-6532

Minnesota Office:14451 Hwy 7, Ste. 202

Minnetonka, MN Tel.: (701) 738-2447Fax: (763) 273-1347

Steve’s Cell: (701) 213-707049